As a target object detection device, there have been fish finders known for detecting a school of fish underwater by transceiving ultrasonic waves and radar apparatuses for detecting a target object by transceiving radio waves. For example, a fish finder transmits ultrasonic waves in a depth direction underwater and receives an echo signal from a target object (e.g., a school of fish), and detects the target object. The transception is performed at predetermined time intervals, and the detection result obtained from each transception is sequentially depicted on a display screen while shifting the display position.
With the target object detection device, various displaying methods are proposed to improve visibility in displaying the detected target object. For example, JP2010-281736A discloses a fish finder (target object detection device) is proposed, which displays a plurality of display screens including a single display screen and an enlarged display screen, as well as an area where a region to be enlarged is specified on the single display screen. An operator can easily specify a desired enlarged region by instructing a change of the position and/or the size of the area.
However, with the conventional fish finders (target object detection device) described above, the display direction of the display screen for displaying the single screen and the like is fixed. Generally, within a display area where the single display screen is displayed, the resolution in a vertical direction (depth direction) is set relatively high, whereas the resolution in a horizontal direction (time direction) is set relatively low. Therefore, the display range of echo data with respect to time is fixed and cannot be switched flexibly.